In vitro and in vivo biocontrol of soil-borne phytopathogenic fungi by certain bioagents and their possible mode of action.

The study aimed to investigate new wide-spectrum biological control agents against soil-borne fungal plant pathogens. Screening of 336 fungal strains and 256 bacterial strains was carried out in vitro to select the most promising isolates for controlling destructive pathogens of greenhouse-vegetables. In dual cultures, Bacillus subtilis JF419701 and Trichoderma harzianum JF419706 (teleomorph: Hypocrea lixii) inhibited the growth of Alternaria alternata, Fusarium oxysporum, Exserohilum rostratum, Macrophomina phaseolina, Pythium ultimum and Rhizoctonia solani. Microscopic examination showed the ability of T. harzianum JF419706 to parasitize the hyphae of all pathogens and kill them. T. harzianum produced the cell wall degrading enzymes; α-1-3-glucanase (0.83 U/ml) , β-1-3-glucanase (0.89 U/ml) and chitinase (0.86 U/ml) in high concentrations. However, B. subtilis produced proteases in very high concentrations (9341.64 U/ml) . The culture filtrate of T. harzianum did not show any antifungal effect. The cell free extract of B. subtilis, containing cyano-compounds, suppressed the growth of all phytopathogens, especially M. phaseolina. Results proved the efficacy of the two biological control agents to control the common soil pathogens either singly or in combination. We recommend further field experiments to study either the synergistic or antagonistic interactions between them under natural conditions.